staging: wfx: drop protection for asynchronous join during scan

In former code (before the inclusion of the driver in mainline kernel),
hif_join() could run asynchronously. When a join request was in
progress, it was forbidden to launch hif_scan().

Now, hif_join() is always run synchronously. There is no more reasons to
keep a protection against this case.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200420160311.57323-13-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>